The present invention relates generally to controllers for a combustion system for a gas turbine. In particular, the invention relates to a combustor control algorithm for a Dry Low NOx (DLN) combustor.
Industrial and power generation gas turbines have control systems (“controllers”) that monitor and control their operation. These controllers govern the combustion system of the gas turbine. To minimize emissions of nitric-oxides (NOx), DLN combustion systems have been developed and are in use. Control scheduling algorithms are executed by the controller to operate DLN combustion systems. Conventional DLN algorithms receive as inputs measurements of the exhaust temperature of the turbine and of the actual operating compressor pressure ratio. DLN combustion systems typically rely solely on the turbine exhaust temperature and compressor pressure ratio to determine an operating condition, e.g., turbine exhaust temperature, of the gas turbine.
Conventional scheduling algorithms for DLN combustion systems do not generally take into account variations in ambient operating conditions, such as seasonal variations in ambient air temperature and humidity. Similarly, conventional scheduling algorithms do not account for variations due to compressor inlet pressure loss and variations in the exhaust back pressure of the turbine. Rather, conventional scheduling algorithms generally assume that ambient conditions, e.g., humidity, compressor inlet pressure loss and turbine back pressure remain at certain defined conditions or that variations in these conditions do not affect the target exhaust turbine temperature.
DLN combustion systems for gas turbines generally are sensitive to ambient conditions, such as outside ambient humidity. Seasonal variations in humidity can affect the operation of a DLN combustion system. As the ambient conditions change with the seasons, the settings of DLN combustion systems are often manually adjusted to account for ambient seasonal variations. In addition, compressor inlet pressure loss and turbine back pressure may drift from the loss and pressure levels used to define the DLN combustion settings. The NOx and carbon monoxide (CO) emissions from the gas turbine may increase beyond prescribed limits, if the conventional DLN combustion system is not adjusted as the seasons change or to compensate for variations in the compressor inlet pressure or turbine back pressure.
There is a long felt need for a combustion system controller, and especially a DLN controller, that accommodates seasonal variations in ambient conditions and changes in the inlet pressure and exhaust back pressure. Similarly, there is a long-felt need for a controller that reduces the need to manually adjust the DLN combustion controller of a gas turbine to account for seasonal fluctuations in ambient conditions, and for changes in the inlet pressure loss and turbine back pressure.